Uv-vis spectroscopy instrument and methods for color appearance and difference measurement

ABSTRACT

Embodiments of the invention generally relate to color and appearance metric measurements and, in particular, developing instrumentation to enable self-consistent image appearance measurements within instruments of unitary construction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application or patent claims the benefit of U.S. ProvisionalPatent Application No. 62/654,831, filed Apr. 9, 2018, the completecontents of which are herein incorporated by reference. In the event ofconflicting information between the incorporated content and contentexplicitly provided herein, the latter controls.

FIELD OF THE INVENTION

Embodiments of the invention generally relate to psycho-physicalmeasurements and, in particular, spectroscopy instruments and methodsfor characterizing the appearance of samples in a self-consistent way.

BACKGROUND

Three elements are involved in seeing or perceiving color: a lightsource, an object, and an observer. A framework of describing humancolor perception according to these three elements is sometimes referredto as the visual observing situation. To build an instrument thatquantifies human color perception, each item in the visual observingsituation may be characterized.

The first element of the visual observing situation is a light source. Alight source is a physical source of light. The visible portion of theelectromagnetic spectrum is defined by the

International Commission on Illumination (CIE) as 360 to 780 nm. A plotof the relative energy at each wavelength creates a spectral powerdistribution (SPD) curve that quantifies the characteristics of thelight source. A CIE, illuminant is a standard table of numbersrepresenting relative energy versus wavelength for the spectralcharacteristics of light sources. Some common illuminants and their CIEabbreviations are as follows: Incandescent (A), Average Daylight (C),Noon Daylight (D₆₅), and Cool White Fluorescent (F2). By representing alight source as an illuminant, the spectral characteristics of the firstelement of the visual observing situation is quantified andstandardized.

The second element of the visual observing situation is an object.Objects modify light. Colorants such as pigments or dyes that are in oron the object selectively absorb some wavelengths of incident lightwhile reflecting or transmitting other wavelengths. The amount of lightthat is reflected, absorbed, or transmitted by the object at eachwavelength can be quantified. This can be represented as a spectralcurve. By measuring the relative reflectance or transmissioncharacteristics of an object, the second element of the visual observingsituation becomes quantified. Relative reflectance, or reflectancefactor, is defined as the relative amount of energy measured on anarbitrary sample at a fixed geometry, in reflection, with respect to aknown white sample similarly used to define the top-of-scale of themeasurement. This is important to distinguish as reflectivity is also afunction of angle and total reflectance would require a hemisphere tocollect all angles. A device which measures relative reflectance ortransmittance as a function of wavelength is typically aspectrophotometer.

The third element of the visual observing situation is the observer,which is often but not necessarily a human. A human eye has structuresreferred to as rods and cones. Cones are responsible for color visionand have three types of sensitivity: red, green, and blue. The CIEexperimentally measured the ability of the human eye to perceive color.The experimentally derived x-bar, y-bar, and z-bar color matchingfunctions became the CIE 1931 2° Standard Observer. The functions x-bar,y-bar, and z-bar quantify the red, green, and blue cone sensitivity ofan average human observer. An updated standard was later produced and isreferred to as the 1964 10° Standard Observer. This is the standardrecommended for use today by the CIE.

In science and industry, the trifecta of light source, object, andobserver becomes the trifecta of light source, sample, and detector. TheCIE X, Y, and Z tristimulus color values are obtained by multiplying theilluminant, the reflectance or transmittance of the object, and thestandard observer functions. The product is then summed for allwavelengths in the visible spectrum to give the resulting X, Y, Ztristimulus values.

A colorimetric spectrophotometer may comprise a light source, adiffraction grating, a diode array, and a processor. The instrument maybe configured to produce CIE, X, Y, Z color values for a sample.Briefly, the light source illuminates the sample being measured. Lightreflected by the objects is passed to a diffraction grating which breaksit into its spectral components. Much of the diffracted light falls ontothe diode array which senses the amount of light at each wavelength. Thespectral data is sent to the processor where it is multiplied with auser-selected illuminant and observer tables to obtain CIE X, Y, Z colorvalues.

The CIE X, Y, Z value system is a color scale. When describing color,the CIE X, Y, Z values are not easily understood (they are notintuitive). Other color scales have been developed to better relate tohow humans perceive color, simplify understanding of the metrics,improve communication of color, and better represent uniform colordifferences. All colors can be organized in three dimensions: lightness,chroma or saturation, and hue. Hunter L,a,b color space is a3-dimensional rectangular color based on Opponent-Colors Theory with thefollowing dimensions:

L (lightness) axis: 0 is black, 100 is white, and 50 is middle gray

a (red-green) axis: positive values are red, negative values are green,and 0 is neutral

b (blue-yellow) axis: positive values are yellow, negative values areblue, and 0 is neutral

The opponent-colors have been explained physiologically by theorganization of cone cells into what are called receptive fields in thefovea of the human eye. A receptive field provides a number of inputsfrom the cone cells (both positive and negative) that can interface withganglion cells to produce spatial edge-detection for red-green andblue-yellow stimuli. The spectral distribution for these receptivefields correlates well with a, b.

There are two popular L,a,b color scales in use today: Hunter L,a,b andCIE L*,a*,b*. While similar in organization, a color will have differentnumerical values in these two color spaces. Both Hunter L,a,b and CIE,L*,a*,b* scales are mathematically derived from CIE X,Y,Z values. Scalesof chroma and hue are also functions of a* and b*; where chroma is thescalar magnitude, ((a*)²+(b*)²)^(1/2), and hue angle is represented bythe arc tangent of (b*/a*).

Color measurement is employed in industry and in education according tocolor differences. Color differences are calculated as sample-standardvalues. According to the CIE L*,a*,b* color scale,

If delta L* is positive, the sample is lighter than the standard. Ifdelta L* is negative, the sample is darker than the standard.

If delta a* is positive, the sample is more red (or less green) than thestandard. If delta a* is negative, the sample is more green (or lessred) than the standard.

If delta b* is positive, the sample is more yellow (or less blue) thanthe standard. If delta b* is negative, the sample is more blue (or lessyellow) than the standard.

Total color difference (delta E*, or AE*) is based on the L*,a*,b* colordifferences and was designed to be single number metric for PASS/FAILdecisions in industry. Delta E* is determined as the square root of thesum of the squares of L*, a*, and b*:

(ΔE*=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)}

Thus far color of an object or sample has been generally ascribed topigments or dyes of uniform extent. The use cases when applying delta E*are limited to comparing samples that do not have complicatedsurroundings and are observed under identical viewing conditions. Otherqualities of an object also play a role in color, further complicatingits measurement and characterization. Surface characteristics andgeometry play an important role in color.

Surface characteristics such as high frequency spatial patterns canmodulate perceived color. To accurately measure delta E*, the spatialcharacteristics of the human observer must be further modeled. Thisincludes the spatial frequency response of contrast sensitivityfunctions (CSFs) modeling the eye physiology. Each CSF may be thought ofas a convolution or low-pass filter (in the frequency domain) whenobserved with different sizes of receptive field; of which largereceptive field apertures transfer low spatial frequency stimuli. As aresult, there is a spatial-color sensitivity of the human eye, accordingto red-green, and blue-yellow dimensions. In general, as the spatialfrequency of the stimulus increases (narrower spacing), colordifferences become erroneous, especially differences along theblue-yellow axis. Since the opponent-color spaces like L*, a*, b* aredifferentiable, there exists a direct correlation to the spatialreceptive field and convolutions of the L*, a*, b* axes.

Another surface characteristic of samples is reflectance. For opaquematerials, most of the incident light is reflected or absorbed. Fortranslucent materials, most of the incident light is transmitted.Reflectance make take either of two forms. Diffuse reflection involvesnon-directional reflected light. This light is scattered in manydirections. Specular reflection is reflection of light by which theangle of reflection matches the angle of incidence of the incident lightstriking the surface of the object.

For fluorescent materials, another surface characteristic is the lightemitted by the material as a function of the illuminating source.Fluorescent whitening agents (FWAs), for example, are molecules thatabsorb light in the ultraviolet and violet wavelengths of theelectromagnetic spectrum and re-emit light in blue wavelengths. Theaddition of both reflectance and fluorescence components can greatlyexceed the reference white point. UV adjustments for calibratingwhiteness instruments to materials was developed Ganz and Griesser. TheUV control system was further refined by Imura et al. (U.S. Pat. No.5,636,015), who extended the method to include the multiple excitationof LEDs in (U.S. Pat. No. 8,288,739).

Color is seen in the diffuse reflection, and gloss is seen in thespecular reflection. The reflection at the specular angle is generallythe greatest amount of light reflected at any single angle. Fromair-to-glass at low angles of incidence, specular reflection representsless than 4% of total incident light. For a 60° angle (as in glossgeometry), the reflection of polished glass is ˜10%. The remaining lightis transmitted or absorbed with almost no diffuse reflection.

Richard Sewall Hunter, a pioneer in color and appearance, identified sixvisual criteria for defining a gloss scale. These are specular gloss,contrast gloss, distinctness-of-image (DOI) gloss, absence-of-bloomgloss, sheen, and surface-uniformity gloss. In the color industry,“instrumental gloss” is the most common form of gloss measurement andcorrelates with Hunter's specular gloss criteria. The ratio of diffusereflection (45° to the angle of incidence) to specular reflection (equalto the angle of incidence) if subtracted from unity is a measure ofcontrast gloss. An exemplary geometry for measuring instrumental glosson most samples is 60° (i.e., 60/60, defined with respect to the surfacenormal of the sample). Another geometry (30/30) has combined multiplefield angles with a diode array to quantify reflection haze anddistinctness of reflected image (DORI).

Surface texture of samples can greatly affect perceived color. Sampleswhich have exactly the same color to a spectrophotometer, but which havedifferent surface textures, will appear to have different colors to ahuman observer. Surfaces may generally be described as glossy or matte.Glossy surfaces appear darker or more saturated. Matte surfaces appearlighter and less saturated. Increased surface roughness affectsperceived color such that it appears lighter and less saturated. This iscaused by mixing diffuse reflectance (where humans see pigment color)with increased scatter from specular reflectance (white). The rougherthe surface, the greater the scatter of the specular reflectance.

Instrument geometry defines the arrangement of light source, sampleplane, and detector. There are two general categories of instrumentgeometries: Bi-directional (45°/0° or 0°/45°) and diffuse (d/8° sphere).Bi-Directional 45°/0° geometry has illumination at a 45° angle andmeasurement at 0° . The reciprocal, 0°/45° geometry, has illumination at0° and measurement at 45°. Both directional geometries by definitionexclude the specular reflection in the measurement. This is sometimesindicated in numerical tables by the phrase, “specular excluded”.Bi-Directional geometry measurements provide measurements that maycorrespond to visual changes in sample appearance due to changes ineither pigment color or surface texture. To reduce the directionality ofan arbitrary sample, the 45° illumination or detection may be revolvedcircumferentially around the sample in at least 12 equally spacedlocations (designated as 45c) or ring-shaped beams may be formed usingaxicon lenses or free-form optics (45a).

Diffuse (sphere) geometry instruments use a white coated sphere todiffusely illuminate a sample with 8° (d/8° viewing. Measurements on adiffuse sphere instrument can be taken with the specular included orspecular excluded. Specular included measurements negate surfacedifferences and provide values which correspond to changes in actualcolor (as opposed to perceived color). Specular excluded measurementsnegate specular reflectance on very smooth surfaces, measuring onlydiffuse reflectance. For illustration, as between two surfaces paintedwith the same red paint, one surface having a matte finish and the othersurface having a high gloss finish, the specular included measurementindicates no color difference. It quantifies only colorant differencesand negates differences in surface finishes. In the specular excludedmode, the readings quantify appearance differences, similar to thosefrom the direction (0°/45°) geometry instrument. Most diffuse geometrymeasurements are taken in the specular included mode.

Glossmeters, spectrophotometers, and other imaging devices employed inoptics are traditionally independent instruments. These devices may bespecially tailored to detect and characterize very specific qualities oflight while ignoring other qualities of light. Yet, gloss, reflectance,measured color, perceived color, and texture are all interrelated. Whenthese attributes are characterized separately (e.g., by independentlaboratory instruments like independent glossmeters and independentspectrophotometers), variations in environmental conditions ordevice-dependent parameters inevitably result in inconsistencies amongthe characterizations of the individual attributes. Indeed, theindependent measurements may conflict over the actual appearance of asample.

The “Spectromatch Gloss Spectrophotometer”, available from SheenInstruments, is one example attempt in the industry to combine color andgloss measurements in one unit. Devices such as this still fail toprovide “constant” color difference of a sample, if paired with anexternal imaging system, because the appearance of surface featuresdepends on the luminance distribution of the illumination scene. The twoinstruments exist separately, and information cannot be easilycorrelated together to calibrate consistent results.

SUMMARY

According to one aspect, a single optical instrument (in particular, aspectroscopy instrument) with well-defined geometry and apertures isconfigured for measuring instrumental gloss, relative reflectance, andtwo-dimensional color appearance images in a self-consistent way.

Subsystems responsive for relative reflectance measurement and imagingmay share reciprocal 45/0 and 0/45 geometries of the same sampleaperture (e.g., multiple apertures from 0.1″-2.0″ in diameter). Amotorized rotation stage permits an interchange between illumination andmeasurement axes. That is, in the reciprocal design, illumination at 0°can be interchanged with the imaging system at 0° via the motorizedrotation stage. In both cases, the reciprocal cone angles may beidentical as well as the illumination-detection spectral powerdistributions (SPDs). Self-consistency may mean equating multipleviewing parameters (such as measurement geometry and SPD) between two ormore subsystems, in order to reduce the optimization solution space ofcolor appearance and difference and more easily facilitate accuratecolor reproduction.

According to an exemplary embodiment, a spectroscopy instrumentcomprises, in a unitary construction, a gloss-measuring subsystemconfigured to measure instrumental gloss; a reflectance-measuringsubsystem configured to measure relative reflectance of multiple sampleapertures; and an imaging subsystem configured to capture one or morecolor appearance images and segment the image into multiple regions ofinterest.

An exemplary spectroscopy instrument may further comprise a controller(which may be or include a closed loop control system) configured toself-consistently optimize an image color appearance model (iCAM)dependent on one or more area-averaged color measurement apertures frommeasurements of the gloss-measuring subsystem, reflectance-measuringsubsystem, and imaging subsystem. Self-consistent may mean components ofthe iCAM present non-conflicting characterizations of object or sampleappearance. The method significantly constrains the chromatic adaptationtransform (CAT) equations in image color appearance models (iCAMs).

An exemplary spectroscopy instrument may further comprise a sampleaperture shared by the gloss-measuring subsystem, thereflectance-measuring subsystem, and the imaging subsystem. Thereflectance-measuring subsystem and imaging system may share reciprocal45/0 and 0/45 geometries of the sample aperture. An illumination axis ofthe reflectance-measuring subsystem may be coaxial with a measurementaxis of the imaging subsystem. The sample aperture may be variable from0.1″ to 2″ through a combination of a variable field-stop forillumination and a variable port plate for collection. Ø0.1″ is theaperture diameter of the CIE, 1931 2° stimulus, and Ø2″ represents thebackground aperture diameter for CIE 1964 10° stimulus.

An exemplary spectroscopy instrument may further comprise a controllerfor controlling activation of the subsystems, one or more ultraviolet(UV) light sources of one or more of the subsystems, and one or moresample presence sensors for detecting the presence or absence of asample, wherein the controller is configured to permit activation of theone or more UV light sources only when the presence of a sample isdetected by the one or more sample presence sensors.

An exemplary spectroscopy instrument may further comprise a ringassembly that comprises separate fiber-optic arrays of the reflectancesubsystem and the imaging subsystem.

An exemplary gloss-measuring subsystem may comprise an emitter block anda receiver block with 20/20, 60/60, 85/85 or 30/30 geometry.

An exemplary gloss-measuring subsystem may be ASTM D523 compliant.

An exemplary reflectance-measuring subsystem may comprise anillumination assembly (shared with the imaging subsystem), a fiber-opticdetection array, and a spectrometer. The illumination assembly maycomprise an LED array and a color mixing light pipe for homogenizingdifferent outputs of different LEDs of the LED array. The LED array maycomprise electroluminescent narrow-band full width half maximum (FWHM)LEDs, or electroluminescent LEDs and laser diodes combined withbroadband photoluminescent YAG phosphors or quantum dots.Advantageously, using the same LED array in two subsystems (reflectanceand imaging) achieves self-consistent viewing conditions. The combinedSPD of the LED array may be finely tuned using pulse width modulation tocompensate for differences in the detector spectral response of thesubsystems.

An exemplary spectroscopy instrument may further comprise a controllerfor controlling activation of the subsystems, wherein the controller hasdiscrete control over each LED of the LED array and permits measurementcharacterization of a fluorescing sample emission as a function of itsexcitation.

An exemplary reflectance-measuring subsystem may further comprise aplurality of lens groups. The exemplary reflectance-measuring subsystemmay further comprise a motorized stage for changing which of theplurality of lens groups is aligned with a 0° axis of thereflectance-measuring subsystem.

An exemplary imaging subsystem may comprise an imaging device affixed tothe motorized stage, the motorized stage being movable to bring theimaging system into and out of alignment with the 0° axis. The exemplaryimaging subsystem further comprises equally-spaced circumferentialillumination, wherein the imaging system has a 45c/0 geometry utilizinga secondary fiber-optic array of the ring assembly coupled to theillumination assembly, when the imaging system is in alignment with the0° axis.

An exemplary reflectance-measuring subsystem may be CIE 15:2004 and ASTME1164 compliant. An exemplary imaging subsystem may be ISO 17321compliant. To fully comply with ASTM E1164, collimating optics areneeded to reduce the cone angles to +/−2° about the 45° axis.

An exemplary spectroscopy instrument may comprise a controllerconfigured to self-consistently optimize color spaces and colordifferences from measurements as a function of the aperture size frommeasurements of the gloss-measuring subsystem, reflectance-measuringsubsystem, and imaging subsystem, wherein the controller is configuredto process an image from the imaging subsystem in dependence on thereflectance and gloss measurements, and outputs a self-consistent imageappearance and color difference metrics as a function of aperture sizeat an output terminal. The output terminal may be a user interfaceshared by the gloss-measuring subsystem, the reflectance measuringsubsystem, and the imaging subsystem.

An exemplary spectroscopy instrument may comprise a controllerconfigured to optimize an image appearance and color difference model ofthe gloss-measuring subsystem, reflectance-measuring subsystem, andimaging subsystem self-consistently; wherein the controller isconfigured for initial mapping of information from the relativereflectance to the visual field at multiple area-averaged measurementapertures of increasing size about a stimulus, and multiple viewingconditions are made equal to constrain the total amount of colorimetricshift between subsystems. The controller is configured for initialmapping of the relative reflectance to RAW pixels values of the imagesensor, then separates the spatial characteristics of thetwo-dimensional imagery within a local color difference metric,characterizing spatial content in terms of gradients of the colordifference metrics, and measuring the influence of gloss on objectappearance.

An exemplary spectroscopy instrument may comprise a controller that,after each measurement, is configured to determine whether themeasurement and any preceding cycles of the same measurement satisfy apredetermined minimum statistical certainty, direct the subsystem torepeat the measurement if the predetermined minimum statisticalcertainty is not satisfied, and conclude measurement with the subsystemif the predetermined minimum statistical certain is satisfied. When thedetermining step finds the predetermined minimum statistical certaintyis not met by the measurement, the controller is may adjust one or moremeasurement parameters prior to repeating the measurement.

An exemplary method of producing color and appearance measurements for asample comprises measuring relative reflectance of the sample; measuringinstrumental gloss of the sample; capturing an image of the sample; andoutputting self-consistent color appearance and difference based on themeasured relative reflectance of multiple apertures, the measuredinstrumental gloss, and the captured image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary spectroscopy instrument that includes agloss-measuring subsystem, a reflectance-measuring subsystem, and animaging subsystem in a unitary construction.

FIG. 2A is the instrument of FIG. 1 with the housing and sample clampnot shown.

FIG. 2B is the instrument of FIG. 2A with the sample port plate notshown.

FIG. 3 is a top perspective view of the instrument of FIG. 1 withcertain elements omitted to permit illustration of otherwise obscuredelements.

FIG. 4 is a bottom perspective view of the instrument of FIG. 1 withcertain elements omitted to permit illustration of otherwise obscuredelements.

FIG. 5 is another bottom perspective view of the instrument of FIG. 1with certain elements omitted to permit illustration of otherwiseobscured elements.

FIG. 6 is another top perspective view of the instrument of FIG. 1 withcertain elements omitted to permit illustration of otherwise obscuredelements.

FIG. 7 is a top plan view showing the lens platter in the smallarea-of-view (SAV) measuring position.

FIG. 8 is the view from FIG. 7 but with the optional telecentric lensassembly omitted to permit illustration of the otherwise obscureddigital camera assembly.

FIG. 9 is a top plan view showing the lens platter in the camera imagingposition.

FIG. 10 is a top plan view showing the lens platter in the largearea-of-view (LAV) measuring position.

FIG. 11 is the illumination assembly that provides illumination for thereflectance and imaging subsystems.

FIG. 12 is the illumination assembly with certain elements omitted topermit illustration of otherwise obscured elements.

FIG. 13 is another view of the illumination assembly with certainelements omitted to permit illustration of otherwise obscured elements.

FIG. 14 is an optical diagram which illustrates geometry concerning thereflectance-measuring subsystem.

FIG. 15 is an optical diagram which illustrates geometry concerning thereflectance-measuring subsystem as well as the gloss-measuringsubsystem.

FIG. 16 is an optical diagram which illustrates geometry concerning theimaging subsystem with a large area-of-view (LAV) configured camera.

FIG. 17 is an optical diagram which illustrates geometry concerning theimaging subsystem with a small area-of-view (SAV) configured camera.

FIG. 18 is a functional block diagram for self-consistent colorreproduction that is a function of area-averaged apertures of varyingdiameter.

FIG. 19 is an exemplary self-consistent method performable with thespectroscopy instrument shown in FIGS. 1-13.

FIG. 20 is a diagram of variable apertures of the spectroscopyinstrument at a 130 mm (5.1 in) viewing distance.

FIG. 21 is a block diagram showing relationships of components of thespectroscopy instrument with respective subsystems.

FIG. 22 is a flowchart for an exemplary adaptive measurement process.

DETAILED DESCRIPTION

The figures show different views of an exemplary instrument 100 or partsthereof. FIG. 1 shows instrument 100 in its entirety as viewed from anexterior. At its exterior, instrument 100 includes, for example, a userinterface 101 and sample clamp 102. As the disclosure progresses tosubsequent figures, parts of the instrument 100 are selectively removedfrom view to permit viewing of further parts which are otherwiseobscured. For instance, as compared to FIG. 1, FIGS. 2A and 2B do notshow the housing 103, sample clamp 102, or user interface 101, therebypermitting a view of elements ordinarily enclosed by the housing 103 ina state of use. It should be appreciated that in the practice of theinvention, not all parts shown in the figures must necessarily bepresent. An exemplary embodiment is shown by the figures forillustrative purposes, but the claims below define the scope of theclaimed invention.

FIG. 1 is an exemplary (optical) instrument 100 for applying an imagecolor appearance model and/or components thereof to optimize thereproduction biases of color difference in device-dependent subsystems.The instrument 100 is configured to measure 60° instrumental gloss, 0/45circumferential relative reflectance, and 45/0 two-dimensional colorappearance images (from a reflected luminance) and present thesemeasurements to an image color appearance model of the components ofwhich are self-consistent. Self-consistent means that the components donot present conflicting characterizations of object or sampleappearance. The instrument may also be configured for a 20°, 85°, or 30°gloss measurement.

The configuration of an instrument 100 as described in the precedingparagraph may be achieved by the combination of a gloss-measuringsubsystem, reflectance-measuring subsystem, and imaging subsystem, allthree of which are arranged in a unitary construction. FIG. 21illustrates these three subsystems diagrammatically.

The expression “unitary construction” as used herein may becharacterized in one or more of the following ways. Unitary constructionmay mean all subsystems are part of a single product or device. Unitaryconstruction may involve a common or shared housing which shieldssubsystems from foreign contaminants and certain environmentalconditions. Unitary construction may mean subsystems, or at least partsof subsystems, have fixed spatial relationships with one another thatare substantially unchanging or unchangeable. Unitary construction maymean having shared optical axes. Unitary construction may mean some orall subsystems share a common computerized controller (e.g., a maincontrol board and/or single board computer (SBC)). Unitary constructionmay mean all optical subsystems are configured to measure one or moreaspects of a stationary sample that does not need to be moved fordifferent measurements. This may be achieved with, for example, a commonsample port plate 104 used by some or all optical subsystems.

As a loose analogy, an automobile may be considered of a unitaryconstruction. Doors, windows, power locks, engine, transmission,drivetrain, power steering, entertainment system, CAN bus, frame,headlights, air conditioning system, and so on and so forth—all of theseare subsystems or parts of subsystems which are combined according to aunitary construction. While parts may be interchanged or replaced, andwhile some parts may have some degrees of freedoms with respect to otherparts (e.g., doors pivot with respect to their attachment point on theframe), even a layman may appreciate the unitary construction of theseelements for an automobile.

FIG. 2A shows the instrument 100 with housing 103 and sample clamp 102removed. The sample clamp receiver 201 is configured to receive andretain the sample clamp 102 in a fully assembled state. The sample clampreceiver 201 is configured to adjust a height of the sample clamp 102.The sample port plate 104 is arranged at a top surface of the instrument100 and is configured to receive a sample on its face. The sample portplate 104 contains an aperture 202 in its center through which light maytravel to contact whatever sample is placed atop the sample port plate104. FIG. 2A also shows the main instrument control board 203 whichcontrols activation and management of the subsystems which will bedescribed in connection with subsequent figures.

FIG. 2B shows the instrument 100 with the sample port plate 104 removed.Directly beneath the sample port plate is a sample port plate receiver211. The sample port plate receiver 211 may be configured to receivemultiple sample port plates of different configurations, e.g., plateshaving different aperture diameters. The sample port plates may thus beremovable and interchangeable by a user in a state of use. The sampleport plate receiver 211 comprises sample port plate detectors 212configured to detect the presence and/or absence of a sample plate.

The sample port plate detectors 212 and one or more sample presencesensors are particularly advantageous with respect to safety concerns.In use, the internals of instrument 100 emit light of differentwavelengths, including wavelengths in the ultraviolet (UV) spectrum.Where possible it is advantageous for human users to be shielded fromdirect exposure to UV light. The instrument 100 blocks or substantiallyblocks UV light emissions from the top of the instrument (and thus therisk of human exposure) by the combination of a sample port plate and asample covering the aperture thereof. The instrument 100 may beconfigured to only permit activation of light emitting parts, inparticular UV light emitting parts, when the presence of both a sampleplate and a sample are detected. The sample plate detectors 212 areconfigured to identify whether a sample plate is present. The one ormore sample presence sensors, on the other hand, are configured to sensewhether a sample is present covering the aperture of the sample plate.Emitting parts and detecting parts of one of the instrument's subsystemsmay be used as the sample presence sensors. For example, the samplepresence sensors may involve the light emitting parts of the ringassembly which are discussed in greater detail below. In particular, thefiber-optic illumination array of the ring assembly may be brieflyactivated, and the imaging subsystem detects whether or not light isreflected by a surface at the aperture of the sample plate. Reflectedlight indicates a sample is present, and vice versa. Alternatively, theillumination assembly, fiber optic array, and array spectrometer may beemployed. The illumination assembly may be briefly activated, and thefiber optic array and array spectrometer used to detect whether or not areflected signal is detected. In the absence of a detected reflectancethe instrument may determine no sample is present and therefore preventitself from emitting UV light (at least until the presence of a sampleis detected). Alternatively, a sample presence sensor may be providedvia the gloss-measuring subsystem. The gloss measurement emitter blockmay be briefly activated, and the gloss measurement receiver block isconfigured to detect whether or not the signal has reflected off asample surface. Without a sample at the sample port plate, the glossmeasurement receiver block would not receive a signal corresponding withwhat was emitted by the emitter block. One advantage of using thegloss-measuring subsystem as sample presence sensor is that thegloss-measuring subsystem is comparatively fast and presents a lowerprocessing burden as compared to the reflectance-measuring subsystem andthe imaging subsystem. The sample presence sensor may be activated as aprecursor to every measurement (at least every measurement involving UVradiation) and thus the fastest and least burdensome means of detectionresults in faster and more efficient operation of the overallinstrument.

Below and substantially adjacent to the sample port plate is a ringassembly, shown in FIGS. 3, 4, and 5. The ring assembly 301 comprises afiber-optic detection array 302 (for the reflectance subsystem) and afiber-optic illumination array 303 (for the imaging subsystem). Thefiber-optic illumination array 303 is coupled to the illuminationassembly 414 of the reflectance-measuring subsystem by fiber bundle 312and a relay lens. Immediately adjacent to and symmetrically positionedwith the ring assembly 301 are gloss measurement emitter 305 andreceiver 306 blocks (for the gloss subsystem). A center axis of the ringassembly 301 is vertical (i.e., normal to ground) and is coaxial withthe center axis of the sample port plate. There are no moving parts forthe circumferential fiber-optic detection array 302 or fiber-opticillumination array 303, both of which are installed into one assembly(the ring assembly 301). Further details of the ring assembly 301 andits constituent parts will be discussed below in connection with thevarious optical subsystems (i.e., the gloss-measuring subsystem, thereflectance-measuring subsystem, and the imaging subsystem).

The instrument 100 comprises a gloss-measuring subsystem. Thegloss-measuring subsystem comprises an emitter block 305 and a receiverblock 306, as shown in FIG. 3. The gloss-measuring subsystem has 20°,60°, or 85° geometry and rectangular apertures consistent with ASTMD523, which is incorporated herein by reference. Thus, with respect tothe surface normal of the horizontal sampling plane of the sample portplate, the angle of incidence for light transmitted or received by therespective blocks is 20°, 60°, or 85° . The gloss-measuring subsystemcomprises a light source such as one or more LED sources for CIEIlluminant C. The subsystem further comprises at least two lenses: aprojection lens and a receiver lens. The subsystem further comprises ay-bar color filter. The light source and projection lens are containedin the gloss measurement emitter block. The receiver lens and y-barcolor filter are contained in the gloss measurement receiver block. Thegloss measurement receiver block further comprises a Siliconphotodetector or diode array. The 20°, 60°, or 85° geometry of thegloss-measuring subsystem also has rectangular aperture sizes for eachlens element with specific requirements in accordance with ASTM D523. Analternate 30° gloss geometry includes an array of rectangular aperturesand diode array receiver as shown in ASTM E430, which is incorporatedherein by reference.

Color difference measurement, introduced above, can be measured using abi-directional instrument. A bi-directional instrument will indicate acolor difference that agrees with a basic visual evaluation by the humaneye, but it will not distinguish color between effects of surface finish(e.g., as between two surfaces painted with the same red paint, onesurface having a matte finish and the other surface having a high glossfinish, the matte surface appears lighter and less red). To properlycharacterize these effects, a rigorous bi-directional reflectancedistribution function (BRDF) would be needed at every illuminationangle, viewing angle, and wavelength. BRDF measurements are possible,but the instrumentation is costly due the required complexity.

The instrument 100 comprises a reflectance-measuring subsystem. Thereflectance-measuring subsystem comprises an illumination assembly 414(see e.g. FIGS. 4, 5 and 11), a plurality of lens and lens groupsproviding variable sample apertures (see e.g. FIGS. 7-10 and 12-13), afiber-optic detection array 302 (see e.g. FIG. 3), and a spectrometer404 (co-located with the main instrument control board 203 (see e.g.FIGS. 2A, 2B, 4, and 5). To reduce the directionality of an arbitrarysample, the 45° detection is revolved circumferentially around thesample in at least 15 equally spaced locations, each locationcorresponding with a separate fiber. The fibers 310 from a monitorchannel (see FIGS. 12 and 13) and the fibers 311 from the fiber-opticdetection array 302 of the ring assembly 301 (see FIG. 3) are separatelybundled and input to the spectrometer (see FIG. 4).

The instrument 100 further comprises a controller which is configuredfor operating (e.g., activating) the multiple subsystems and integratingtheir measurements. In the figures, the controller comprises a maininstrument control board 203 and single board computer 603 (SBC) (seee.g. FIG. 6). Alternative controllers or controller configurations maybe employed in different embodiments. The controller may be described asan electronic controller or a computerized controller. A computerizedcontroller comprises one or more processors and may contain memory,input/output devices, and a power system, among other elements. FIG. 2Ashows for example an I/O and power board 204 with features such as apower switch 205. The controller may comprise a combination of hardware,software, and/or firmware. The controller may be configured tocommunicate with one or more external devices, such as an externalcomputer or smart device. The controller permits operation of theinstrument 100 and generation of a self-consistent iCAM without thesupport of any external hardware, with the exception of a power sourcesuch as a standard wall outlet.

A computerized controller may further comprise image processing means(e.g., programming or algorithm). One image processing may be histogramequalization to enhance local contrast (and allow for correlation of aspectral signature), in addition to tone mapping that is already used incolor appearance models for higher dynamic range (for example,CIECAM02).

Variable sample apertures (of diameters which are 0.1″ to 2″) areprovided using two switchable lens assemblies and a variable field-stop.The two lens groups are identified in FIGS. 7-10 as small area-of-view(SAV) illumination lens group 701 and large area-of-view

(LAV) illumination lens group 702. The SAV illumination lens group 701is configured for 0.1″-1″ sample apertures, and the LAV illuminationlens group 702 is configured for 1″-2″ apertures. The apertures areuser-selectable. The aperture system is analogous to a zoom lens, butallows for the transfer of wider-angle LED emission (120° full width athalf max (FWHM)) with an efficiency up to 70%. At least 16 LEDs can besupported within the field of view of the illumination in a 0.25″×0.25″square footprint.

The multiple lens groups are fixedly secured to a motorized lens platter705. The motorized lens platter 705 is rotatable about a fixed axisusing an optical encoder 706, stepper motor 612 (visible in FIG. 6), andcurved gear rack 707. The motorized lens platter 705 is configured topermit a plurality of optical elements arranged thereon to beinterchangeably positioned along a 0° axis along which light travelsfrom the illumination assembly 414 of the reflectance-measuringsubsystem (see e.g. FIG. 11) to the ring assembly 301 and sample portplate 104 above. The 0° axis of the reflectance-measuring subsystem iscoaxial with the center axes of the ring assembly 301 and sample portplate 104.

FIG. 7 shows the SAV illumination lens group 701 aligned with the 0°axis. The 0° axis comes out of the page in FIGS. 7, 8, 9 and 10. FIG. 8is similar to FIG. 7 but hides a telecentric lens assembly 708 to permitview of the digital camera assembly 811 arranged beneath the telecentriclens assembly 708. Some embodiments may have the telecentric lensassembly 708, while other embodiments may not. FIG. 9 shows thetelecentric lens assembly 708 and camera assembly 811 aligned with the0° axis. FIG. 10 shows the LAV illumination group 702 aligned with the0° axis. The alignment of the lens groups with the 0° axis is highlycontrolled for precision and accuracy via the optical encoder 706,stepper motor 612, curved gear rack 707, and lens platter optical limitswitches 712.

FIG. 11 shows the illumination assembly 414 for thereflectance-measuring subsystem. The position of the illuminationassembly 414 within the instrument 100 is shown in FIGS. 4 and 5. Abeamsplitter 1214 supplies light produced from the illumination assembly414 both vertically along the Odeg axis (see description of FIGS. 7-10above) and perpendicularly to a monitor channel 1101. The monitorchannel 1101 is optically connected with the spectrometer 404 by fiberbundle 311 (see FIG. 4).

FIGS. 12 and 13 show the internals of the illumination assembly 414. AnLED array 1212 is arranged at a bottom of the illumination assembly 414on a printed circuit board 1211 (PCB). The LED array 1212 may be highlycompact, e.g., having at least 16 or more LEDs within a 0.25″ by 0.25″surface area. Respective LEDs emit different wavelengths of light, anddifferent combinations of the LEDs may be activated to achieve any of awide range of different outputs. Above the LED array 1212 is a colormixing light pipe 1213 (e.g., a polished square glass rod) configured tohomogenize light emitted from a plurality of LEDs of the LED array 1212for uniform CIE Illuminant D65 output, including ultra-violet light360-400 nm for measuring fluorescent whiting agents. The LED array 1212is controllable to output a variety of different illuminants. The UVcontent is controlled by discrete ˜10 nm FWHM LEDs, with centerwavelengths such as 365, 380, and 395. The instrument 100 has discretecontrol over each LED which enables the measurement characterization ofa fluorescing sample emission as a function of its excitation.

In addition to the LED array 1212 and light pipe 1213, the illuminationassembly 414 further comprises a reference channel beamsplitter 1214, afield stop 1215 with a variable field stop iris (e.g., factory-set oradjustable with motorized gear 1216), an illumination focusing lens1217, and a sample channel iris 1218 (e.g., factory-set or motorized).The reference channel monitors fluctuations in the light output of theLED sources. The PCB 1211 which comprises the LED array 1212 has one ormore heat sinks 1220 to dissipate heat from the LED array 1212, therebyencouraging constant temperature conditions within the instrument 100.

Light emitted from the illumination assembly 414 is transmittedvertically through the instrument along the 0° axis. The light pathpasses through one of the lens groups 701 or 702 of the motorized lensplatter 705, whichever is positioned on the 0° axis for a particularsample measurement. After the lens group the light path reaches thesample (arranged at the aperture 202 of the sample port plate 104), andreflectance therefrom is collected by the fiber-optic detection array302. The fiber-optic detection array 302 is a circumferential ring offibers bundled into one common output for the array spectrometer 404(co-located with the main instrument control board 203, see FIG. 4).There is a reference channel in the array spectrometer 404 that monitorsfluctuations in the LED sources.

The instrument 100 further comprises an imaging subsystem configured tocapture one or more two-dimensional color appearance images. The imagingsubsystem comprises a camera assembly 811 in the 45/0 geometry with acircumferential fiber-optic illumination array 303 embedded in the samering assembly 301 as the fiber-optic detection array 302 of thereflectance-measuring subsystem. The fiber-optic illumination array 303of the imaging subsystem may comprise, for example, five or more fiberillumination ports evenly spaced about the ring assembly 301 (see FIG.3). The imaging subsystem comprises within the camera assembly 811 animage sensor, lens attachment, and the fiber illumination coupler 813comprising a relay lens adjacent to 1217. The coupler 813 opticallycouples the illumination assembly 414 with a fiber bundle 312 (visiblein FIG. 3) when the camera assembly 811 is arranged in the 0° axis ofthe reflectance subsystem. The fiber bundle 312 guides light generatedfrom the illumination assembly 414 to the fiber-optic illumination array303 by total internal reflection. As a result both the reflectancesubsystem and the imaging subsystem may use the same light source. Usingthe same LED array 1212 in two subsystems assists in achievingself-consistent viewing conditions.

The image sensor may be, for example, a charge-coupled device (CCD),complementary metal-oxide-semiconductor (CMOS), or some variant of oneor both of these. The image sensor may take any of a number ofconfigurations, including but not limited to RGB or multispectral colorfilters arrays, linear variable filters, and dispersive forms ofhyperspectral imaging. The most native digital image sensor format isthe RAW pixel output created by the color filter array that is attachedto the sensor. Furthermore, to properly characterize the RAW pixeloutput, any gamma correction of the luminance and tristimulus valuesshould be equal to unity, which is represented by the term RAW/linear.

The camera assembly's image sensor is calibrated to the relativereflectance measurement (of the reflectance-measuring subsystem) andinstrumental gloss measurement (of the gloss-measuring subsystem). Morespecifically, the image sensor output is calibrated to both a relativereflectance measurement (averaged over one or more sample apertures viaa variable field-stop), and an instrumental gloss measurement (averagedover one or more sample apertures in the same range via a variableaperture-stop). Traditional calibration of cameras uses known standards(such as the Macbeth color-chart) to calibrate the variations acrossdevice-dependent sensors.

For a successful calibration, it is important for the same experimentalconditions to be reproduced as much as possible (such as geometry andthe illumination-detection spectrum). The self-consistent instrument 100performs this process in-situ by minimizing the color difference errorbetween the image sensor and the relative reflectance measurement.

An output of the imaging subsystem (or a part thereof) is an array ofcolor differences, corresponding to the error at each pixel.Historically the color difference metrics have been developed forcomparing solid color patches under precise viewing conditions. If asample were to have a complex shape, however, then the color differencewould no longer be valid as information can be lost due to averaging.Therefore, for an exemplary instrument 100, in addition to the initialmapping of the relative reflectance to the image sensor RAW/linear pixelvalues, an image color appearance model (iCAM) is used to separate thespatial characteristics of the two-dimensional imagery within a localcolor difference metric. By starting with a self-consistent image sensorusing average reflected color, the spatial content can then becharacterized in terms of gradients of the color difference metrics(i.e. ∇L*, ∇a*, ∇b*, where the nabla symbol (∇) represents differentialoperators applied to the two-dimensional image), as well as measuringthe influence of gloss on object appearance.

FIG. 14 is an optical diagram which illustrates geometry concerning thereflectance-measuring subsystem. Light from the illumination assembly414 is transmitted upward along the 0° axis. After passing through theLAV lens group 702, the light strikes the surface of the sample ataperture 202. The light which reflects along the 45° direction reachesthe fiber-optic detection array 302 of the ring assembly 301 and iscollected thereby and transmitted to the array spectrometer 404. WhileFIG. 14 is depicted in two-dimensions, it should be appreciated that thefiber-optic detection array 302 has fibers circumferentially arrangedabout the ring assembly 301 so that light reflected along any 45°direction may be collected by the fiber-optic detection array.

FIG. 15 is an optical diagram which illustrates geometry concerning thereflectance-measuring subsystem as well as the gloss-measuringsubsystem. Note that the SAV lens group 701 is used in FIG. 15 whereasthe LAV lens group 702 was used in FIG. 14. The SAV lens group focusesthe light beam, as illustrated in FIG. 15. As in FIG. 14, thefiber-optic detection array 302 collects reflected light per a 0/45geometry. Gloss emission and gloss detection uses a 60/60 geometry. FIG.15 illustrates that the reflectance-measuring subsystem (while employingthe SAV lens group 701) and the gloss-measuring subsystem may involvethe same sample aperture size.

FIGS. 16 and 17 are optical diagrams which illustrate geometryconcerning the imaging subsystem. The sensor pixel data of the imagingsubsystem may also be segmented into multiple area-of-viewconfigurations, e.g. a small area-of-view (SAV) configuration and largearea-of-view (LAV) configuration. The corresponding geometries of thelight beams associated with an LAV-configured camera and aSAV-configured camera are shown in FIGS. 16 and 17, respectively. Theimaging subsystem has a 45/0 geometry, allowing it to overlap inphysical space with the 0/45 geometry of the reflectance-measuringsubsystem. The motorized rotation stage (platter 705) permits aninterchange between the illumination axis of the reflectance-measuringsubsystem and the measurement axis of the imaging subsystem. That is, inthe reciprocal design, illumination by the illumination assembly 414(FIG. 11) at 0° can be interchanged with measurement by the digitalcamera assembly 811 at 0° via the motorized rotation stage.

An exemplary output of an instrument 100 is an image color appearancemodel (iCAM). FIG. 18 is a functional block diagram which highlightsmeasurements and color metrics associated with an exemplary iCAM. Therelative reflectance and instrumental gloss measurands drive theexisting parameters of the iCAM, which initially derive from the cameradevice-dependent color space. Existing literature methods (includingmultiple linear regression) are used for characterizing the image sensorto enable inference of spatial spectral reflectance and colorimetricdata (especially delta-E* with respect to a reference). By applying iCAMmethods, an inferred spatial spectral reflectance can be extracted fromintegrated spectral data when weighted with the derived spatialparameters of the camera image and known spectral components from therelative reflectance measurement across multiple apertures; or withderived gloss characteristics from the known instrumental glossmeasurement. Extensions of iCAM or other sample information may also oralternatively be output. An instrument 100 may provide edge-detectioncontrast. Edge-detection that is implicit in the spatial derivatives ofL*, a*, b* is another extension of iCAM (spatial localization) thatwould allow the instrument user to analyze local color variations intheir sample based on user-defined thresholds for ∇L*, ∇a*, ∇b*. Theunification of all three subsystems enables a constant color differenceof the sample. Constant color difference ∇E* can be realized bymathematical formulation of the viewing conditions between instruments.In this framework, the color difference equation is optimized in a colorappearance space. An image color appearance model can, among otherfunctions, compare color differences measured with different viewingconditions. For example, any change in the spectral power distributionof the illumination between instruments will yield a colorimetric shiftthat must be accounted to achieve a constant color difference ∇E*.

Image color appearance models that account for changes in viewingconditions can adapt the color of the illumination (white point), theillumination level (luminance), and surrounding relative luminance ofthe instrument. Also known as adaptive gain control, these physiologicalmechanisms turn down the gain when the stimulus amplitude is high and byturning up the gain when the stimulus amplitude is low. This advancedcolorimetric tool divides the viewing field of the human observer intomultiple concentric apertures with annuli about a stimulus, as viewedfrom a standard distance of 130 mm or approximately 5.1″ away.

The stimulus of interest is taken to be an area-averaged patch of 2°angular subtense (Ø0.1″ @ 5.1″ viewing distance) according to the CIE1931 standard observer. Larger stimuli use the CIE 1964 supplementarystandard for a 10° angular subtense (Ø0.9″ @ 5.1″ viewing distance).Some examples of the concentric rings about the stimulus include: aproximal field (if defined), a background, and a surround. The proximalfield is the immediately adjacent environment of the stimulus, extending2° from the edge of the stimulus. This region may be used to model localcontrast effects, if useful. The background is defined as the greaterenvironment around the stimulus, extending 10° from the edge of thestimulus or proximal field. Background is used to model simultaneouscontrast. Lastly, the surround is the outside area beyond the sample,but still within the field of view of the imaging system.

An exemplary framework of image color appearance models is described byFairchild (M. D. Fairchild and G. M. Johnson, “The iCAM framework forimage appearance, image differences, and image quality,” Journal ofElectronic Imaging, 13 126-138 (2004)). To explain the method, it ishelpful to further define the convolution operator for an imagingsystem. Convolution is a technique that describes the observationthrough a limiting aperture or kernel filter (i.e., receptive field).The actual mathematics of convolution are given in the followingsequence:

Reverse the kernel

Shift the kernel through the image

Multiply and integrate the kernel with the image

The result of convolution is a “blurred” version of the original image.The process may also be described as a simple multiplication of alow-pass filter in the frequency domain, following a Fourier Transformof the image.

Salient features of the Fairchild implementation include: lightadaptation, chromatic or spectral adaptation, spatial frequencyadaptation, and spatial localization. Light adaptation corresponds to adecrease in visual sensitivity upon an increase in the overall level ofillumination. Chromatic adaptation includes adapting the white point bya weighted combination of the color of the light source and backgroundto reduce changes relative to the spectral power distribution (SPD).Spatial frequency adaptation refines the contrast sensitivity functionequations of the human visual response to appropriately blur highfrequency content, and spatial localization improves the contrast ofedges.

The input to iCAM is pixel image data in absolute luminance units, inaddition to the relative CIE, XYZ values per pixel. The adaptingstimulus is a low-pass filtered CIE, XYZ image that includes absoluteluminance profiles for modeling chromatic adaptation. The absoluteluminance Y pixels are used as a second low-pass image that describe theseveral dependent aspects of the model, such as the Hunt effect(increased image color with luminance) and the Stevens effect (increasedimage contrast with luminance). A third low-pass filter of luminance Yis applied for the image contrast that is a function of the relativeluminance of the surround (Bartleson and Breneman equations). The outputof the model includes a low-pass image, correlates of appearance(brightness, lightness, colorfulness, chroma, hue, saturation) and colordifference. Images are reconstructed to create a color appearance mapthat encodes the apparent color of each pixel in the image for itsviewing conditions. Difference metrics in these appearance dimensionscan be used to derive metrics including delta E* and nabla E*.

FIG. 19 is an exemplary method 1900 of self-consistent methodperformable with an instrument 100, for example. Generally, processesfor producing a self-consistent iCAM may entail first measuring relativereflectance and gloss, and then processing a camera's captured image independence on the reflectance and gloss measurements.

For samples of non-uniform spatial color that are less than 2″ indiameter, and that have a stimulus of interest less than or equal to0.9″ in diameter, as viewed from 5.1″ distance, a self-consistentmeasurement can be taken following a standardization to the top-of-scaleof each subsystem (e.g. black glass for gloss factor and white diffuserfor reflectance factor/white balance of imaging luminance factor). Forthe initial stimulus aperture,

-   -   Standardize and Measure 0/45 XYZ (area-average) (block 1901)    -   Standardize and Measure 60/60 gloss (area-average) (block 1902)    -   Standardize and Measure 45/0 XYZ pixel array of image (block        1903)    -   Estimate color appearance based on image color appearance model        weighted with the above parameters for the initial aperture        (1904)        Then, for each incremental aperture (within a predetermined        aperture range, there being for example at least 2, at least 10,        or at least 20 increments each of which may be equal in size or        some of which may differ in size from one another),    -   Measure 0/45 XYZ (area-average) (block 1905)    -   Estimate color differences of integrated spectral data within        the annulus defined by the increment in aperture, that is        weighted with the derived spatial parameters of the 45/0 XYZ        pixel array and known spectral components from the 0/45 XYZ        (area-average) (block 1906)        These steps may be done automatically in rapid succession from        0.1″ to 2″ with a motorized iris for example on the sample        aperture. Multiple sample apertures are needed to characterize        the proximal, background, and surround conditions for iCAM. FIG.        20 shows the range of aperture values corresponding to each        field. Statistics such as describing the mean error may be used        to optimize color differences extracted from the iCAM and        relative reflectance/gloss.

FIG. 20 illustrates variable sample apertures that may be used for anexemplary instrument 100. A distinction can be drawn between a diameterof interest (of a sample) and background area to the sample of interest.Background area may be interchangeably referred to as proximal area. ForiCAM to be meaningful, analysis of the background content is generallyneeded in addition to analysis of the sample diameter of interest. The“sample aperture” for a measurement depends on the setting of thevariable field stop (e.g., field stop 1215, see FIGS. 12 and 13) and theport size of whichever sample port plate (e.g., sample port plate 104,see FIG. 1) is arranged at the sample port plate receiver (e.g., sampleport plate receiver 211, see FIGS. 2A and 2B). The three opticalsubsystems discussed above (gloss-measuring, reflectance-measuring, andimaging) all share the same sample aperture for at least the smalldiameters (0.1″-0.5″). Relative reflectance and camera/imagingsubsystems also use larger sample apertures of sizes up to theinstrument's maximum sample aperture size, which in the illustratedexemplary embodiment is 2″.

FIG. 21 is a diagram which generally conveys the relationship ofphysical components and physical aspects of an exemplary instrument 100with respect to what is measured or taken:

instrumental gloss, relative reflectance, or an image. FIG. 21 includesa number of features discussed above but is not intended to beexhaustive (i.e., it does not necessarily identify every possiblefeature or aspect of overlap of the subsystems). While some componentsare identifiable with just one of the particular subsystems, asignificant number of components and features correspond with two orthree subsystems. This high level of integration permits the advantagesdiscussed elsewhere in this disclosure, in particular the ability toproduce a self-consistent iCAM for any sample from a single unitarytabletop device.

The instrument 100 is configured to be compliant with standards whichare generally required in industry for gloss measurements andreflectance measurements, for example. In some embodiments, theinstrument is compliant with ASTM D523 for gloss. In some embodiments,the instrument is fully compliant or partially compliant with CIE15:2004 and ASTM E1164 for relative reflectance. Both CIE, 15:2004 andASTM E1164 are herein incorporated by reference. For instance, thefiber-optic array may have collimating elements such as plano-convexlenses or off-axis parabolic mirrors, or the fibers may be replaced withannular 45a ring-shaped beam forming axicon lenses or other free-formoptics, to fully comply with CIE 15:2004 and ASTM E1164. Alternatively,these particular features may be omitted with all other requirements ofCIE 15:2004 and ASTM E1164 still being met. In some embodiments, theinstrument is compliant with ISO 17321 for the image sensor. ISO 17321is incorporated herein by reference.

The instrument may be configured such that ambient conditions such astemperature, humidity, and various forms of environmental noise aresimilarly if not identically regulated for all three subsystems. Theunitary construction is at least partly responsible for this feature;the common housing for all three subsystems encourages consistentregulation of conditions for all of the instrument's internalcomponents. Internal components which may affect ambient conditions,such as the LED array of the illumination assembly which may be capableof generating significant amounts of heat, are regulated by localregulatory means such as heat sinks.

Some embodiments may comprise performing or hardware configured toperform one or more adaptive measurement processes. For example, thesignal of each measurement in real time may be considered, and adetermination made of whether the sample presented is a fluorescent orsimilar high brightness sample. If it is determined to be such a sample,by evaluating the signal characteristics against pre-determinedcriteria, the measurement mode is adjusted and the measurement isautomatically taken in that mode before presenting the measurementresult.

FIG. 22 is a flowchart for an exemplary adaptive measurement process2200. The process 2200 may be employed in connection with a measurementby one, some, or all of the subsystems discussed above. An advantage ofprocess 2200 is the automatic adjustment of repeat sample measurements,the total number of measurement cycles (and parameters of those repeatmeasurements) being adapted for the characteristics of a particularsample. For a single measurand (be it relative reflectance, instrumentgloss, image, or some other measurand), the measurement may need to berepeated a plurality of times to reach a predetermined statisticalcertainty (e.g., to comply with certain industry standards). As agenerality, lighter or more opaque samples require fewer repeatmeasurements, while darker or more transparent samples require a greaternumber of repeat measurements. For example, two common calibrationsamples are a white tile and a black tile. The white tile has a greatdeal of reflectance and can generate a large amount of data with a highdegree of statistical certainty of its accuracy on just one or a fewmeasurement cycles. By contrast, a black tile has very littlereflectance and thus the collected data from a single measurement cyclehas considerably less certainty. An exemplary instrument 100 may beconfigured (e.g., programmed by software and/or firmware in thecontroller) to perform process 2200 in order to automatically andadaptively make a required number of repeat measurements for eachmeasurand. The exact number of repeat measurements may vary from onesample to another. A measurement is taken for a particular measurand atblock 2201. This measurement may be any of the measurements alreadydiscussed above in connection with the various subsystems of instrument100. The controller then checks whether the results of the measurement(or measurements, if more than one cycle has already been performed)satisfy a minimum predetermined statistical certainty. If no, themeasurement at block 2201 is repeated. If yes, then the controller mayconclude its iterative measurement for the specific measurand inquestion and proceed to the next measurand and/or proceed with furtheranalysis of the data which has been collected.

In some instances, prior to repeating a measurement, one or moremeasurement parameters may be adjusted by the controller at block 2204.For example, the lighting conditions of whichever subsystem is beingused may be varied depending on the properties of the specific sample inquestion. Block 2204 serves to improve the results of individualmeasurements (block 2201), while the recursive or repetitive nature ofthe loop in process 2200 ensures an adequate total number of samples forsatisfying overall statistical certainty for the measurand in question.

An exemplary instrument 100 may collect a measure for each ofinstrumental gloss, relative reflectance, and an image for a samplerelatively quickly (e.g., in approximately 25 ms or less). Despite thespeed of a single cycle, an unnecessarily large number of cycles reducesoverall efficiency of the instrument. If a user must manually make adecision as to how many measurement cycles are performed for a givensample, this is not only an inconvenience to a user but also introducesproblems of time delay to allow human computation and the possibility ofhuman error. The automated and adaptive process 2200 eliminates theseconcerns and maximizes the efficiency of producing an iCAM for anysample regardless of the sample's unique aspects as compared to othersamples.

Some embodiments may be a system, a method, and/or a computer programproduct. The computer program product may include a computer readablestorage medium (or media) having computer readable program instructionsthereon for causing a processor to carry out aspects of the presentinvention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Some aspects of some embodiments are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products. It will be understood thateach block of the flowchart illustrations and/or block diagrams, andcombinations of blocks in the flowchart illustrations and/or blockdiagrams, can be implemented by computer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowcharts and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments. In this regard, each block in the flowchart or blockdiagrams may represent a module, segment, or portion of instructions,which comprises one or more executable instructions for implementing thespecified logical function(s). In some alternative implementations, thefunctions noted in the block may occur out of the order noted in thefigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. It will also be noted that each block of the block diagramsand/or flowchart illustration, and combinations of blocks in the blockdiagrams and/or flowchart illustration, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts or carry out combinations of special purpose hardware and computerinstructions.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the invention, subject toany specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present invention, representativeillustrative methods and materials are described.

It is noted that, as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. It is further noted that the claimsmay be drafted to exclude any optional element. As such, this statementis intended to serve as antecedent basis for use of such exclusiveterminology as “solely,” “only” and the like in connection with therecitation of claim elements, or use of a “negative” limitation.

While one or more exemplary embodiments of the present invention havebeen disclosed herein, one skilled in the art will recognize thatvarious changes and modifications may be made, including combinations ofjust some of the elements or features disclosed herein with or withoutadditional elements, without departing from the scope of the inventionas defined by the following claims.

REFERENCE LIST

-   100 instrument-   101 user interface-   102 sample clamp-   103 housing-   104 sample port plate-   201 sample clamp receiver-   202 aperture-   203 main instrument control board-   204 1/0 and power board-   205 power switch-   211 sample port plate receiver-   212 sample port plate detectors-   301 ring assembly-   302 fiber-optic detection array-   303 fiber-optic illumination array-   305 gloss measurement emitter block-   306 gloss measurement receiver block-   310 fiber bundle (from monitor channel)-   311 fiber bundle (from fiber-optic detection array)-   312 fiber bundle (to fiber-optic illumination array)-   404 spectrometer-   414 illumination assembly-   603 single board computer (SBC)-   612 stepper motor-   701 small area-of-view (SAV) illumination lens group-   702 large area-of-view (LAV) illumination lens group-   705 motorized lens platter-   706 optical encoder-   707 curved gear rack-   708 telecentric lens assembly-   712 optical limit switch-   811 digital camera assembly-   813 fiber illumination coupler-   1101 monitor channel-   1211 printed circuit board (PCB)-   1212 LED array-   1213 light pipe-   1214 beamsplitter-   1215 (variable) field stop-   1216 motorized gear-   1217 illumination focusing lens-   1218 sample channel iris-   1220 heat sink

We claim:
 1. A spectroscopy instrument, comprising: in a unitaryconstruction, a gloss-measuring subsystem configured to measureinstrumental gloss; a reflectance-measuring subsystem configured tomeasure relative reflectance; and an imaging subsystem configured tocapture one or more color appearance images.
 2. The spectroscopyinstrument of claim 1, further comprising a controller configured togenerate a self-consistent image color appearance models (iCAMs) frommeasurements of the gloss-measuring subsystem, reflectance-measuringsubsystem, and imaging subsystem.
 3. The spectroscopy instrument ofclaim 1, further comprising a sample aperture shared by thegloss-measuring subsystem, the reflectance-measuring subsystem, and theimaging subsystem.
 4. The spectroscopy instrument of claim 3, whereinthe reflectance-measuring subsystem and imaging system share reciprocal0/45 and 45/0 geometries of the sample aperture.
 5. The spectroscopyinstrument of claim 4, wherein an illumination axis of thereflectance-measuring subsystem is coaxial with a measurement axis ofthe imaging subsystem.
 6. The spectroscopy instrument of claim 3,wherein the sample aperture is variable from 0.1″ to 2″ through acombination of a variable field-stop for illumination and a variableport plate for collection.
 7. The spectroscopy instrument of claim 2,wherein self-consistent means components of the iCAM presentnon-conflicting characterizations of object or sample appearance.
 8. Thespectroscopy instrument of claim 1, further comprising a controller forcontrolling activation of the subsystems, one or more ultraviolet (UV)light sources of one or more of the subsystems, and one or more samplepresence sensors for detecting the presence or absence of a sample,wherein the controller is configured to permit activation of the one ormore UV light sources only when the presence of a sample is detected bythe one or more sample presence sensors.
 9. The spectroscopy instrumentof claim 1, further comprising a ring assembly with a fiber-opticdetection array of the reflectance subsystem, and a fiber-opticillumination array of the imaging subsystem that is coupled to anillumination assembly shared by the reflectance subsystem, wherein thering assembly enables self-consistent viewing conditions in terms ofgeometry and spectral power distribution.
 10. The spectroscopyinstrument of claim 1, wherein the gloss-measuring subsystem comprisesan emitter block and a receiver block with 20/20, 60/60, 85/85, or 30/30geometry.
 11. The spectroscopy instrument of claim 1, wherein thegloss-measuring subsystem is ASTM D523 compliant.
 12. The spectroscopyinstrument of claim 1, wherein the reflectance-measuring subsystemcomprises an illumination assembly, a fiber-optic detection array, and aspectrometer.
 13. The spectroscopy instrument of claim 12, wherein theillumination assembly comprises an LED array and a color mixing lightpipe for homogenizing different outputs of different LEDs of the LEDarray.
 14. The spectroscopy instrument of claim 13, further comprising acontroller for controlling activation of the subsystems, wherein thecontroller has discrete control over each LED of the LED array andpermits compensation for differences in a detector spectral response ofthe subsystems by using pulse width modulation.
 15. The spectroscopyinstrument of claim 13, wherein the LED array comprises one or more ofelectroluminescent narrow-band full width half maximum (FWHM) LEDs,electroluminescent LEDs and laser diodes combined with broadbandphotoluminescent YAG phosphors, and quantum dots.
 16. The spectroscopyinstrument of claim 12, wherein the reflectance-measuring subsystemfurther comprises a plurality of lens groups.
 17. The spectroscopyinstrument of claim 16, wherein the reflectance-measuring subsystemfurther comprises a motorized stage for changing which of the pluralityof lens groups is aligned with a 0° axis of the reflectance-measuringsubsystem.
 18. The spectroscopy instrument of claim 17, wherein theimaging subsystem comprises a camera affixed to the motorized stage, themotorized stage being movable to bring the camera into and out ofalignment with the 0° axis.
 19. The spectroscopy instrument of claim 18,wherein the imaging subsystem further comprises a circumferentialfiber-optic illumination array coupled to the same illumination assemblyof the reflectance-measuring subsystem, wherein the camera has a 45/0geometry with the circumferential fiber-optic illumination array whenthe camera is in alignment with the 0° axis.
 20. The spectroscopyinstrument of claim 1, wherein the reflectance-measuring subsystem isCIE, 15:2004 and ASTM E1164 compliant.
 21. The spectroscopy instrumentof claim 1, wherein the imaging subsystem is ISO 17321 compliant. 22.The spectroscopy instrument of claim 1, further comprising a controllerconfigured to generate a self-consistent image color appearance model(iCAM) from measurements of the gloss-measuring subsystem,reflectance-measuring subsystem, and imaging subsystem, wherein thecontroller is configured to process an image from the imaging subsystemin dependence on the reflectance and gloss measurements, and output aself-consistent iCAM at an output terminal.
 23. The spectroscopyinstrument of claim 22, wherein the output terminal is a user interfaceshared by the gloss-measuring subsystem, the reflectance measuringsubsystem, and the imaging subsystem.
 24. The spectroscopy instrument ofclaim 1, further comprising a controller configured to generate aself-consistent image color appearance model (iCAM) from measurements ofthe gloss-measuring subsystem, reflectance-measuring subsystem, andimaging subsystem, wherein the controller is configured for initialmapping of the relative reflectance to RAW/linear pixels values of theimage sensor, separating the spatial characteristics of thetwo-dimensional imagery within a local color difference metric,characterizing spatial content in terms of gradients of the colordifference metrics, and measuring the influence of gloss on objectappearance.
 25. The spectroscopy instrument of claim 1, wherein for atleast one the subsystems, after each measurement the controller isconfigured to determine whether the measurement and any preceding cyclesof the same measurement satisfy a predetermined minimum statisticalcertainty, direct the subsystem to repeat the measurement if thepredetermined minimum statistical certainty is not satisfied, andconclude measurement with the subsystem if the predetermined minimumstatistical certain is satisfied.
 26. The spectroscopy instrument ofclaim 25, wherein when the determining step finds the predeterminedminimum statistical certainty is not met by the measurement, thecontroller is configured to adjust one or more measurement parametersprior to repeating the measurement.
 27. A method of producing an imagecolor appearance model (iCAM) for a sample, comprising: measuringrelative reflectance of the sample; measuring instrumental gloss of thesample; capturing an image of the sample; and outputting aself-consistent iCAM based on the measured relative reflectance, themeasured instrumental gloss, and the captured image.